I live in Washington State and will be dying soon from terminal cancer. in about 1 month.

MY ONLY ADULT SON LIVES IN Massachusetts.

Previously because my SMALL SS income (sole iincome for 7 years) were all under $25,000, I did hot file taxes 1040 0is year and last year (2014/2015), and since I am dying, I decided to cash out from Fidelity my $60,000 (401K) ROLLOEVER ACCOUNT, WHICH now includes the 2015 Social Security income making is a larger overall income amount.

I live in Washington State. My only adult son lives in Boston. They file their own taxes.

I have asked him to take care of filing my taxes in 2016 for the year 2o15 and he has agreed. We are guesstimating to owe the IRS around 10,000 in my taxes, which we have and have saved for.
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I am filing single . Our taxes will be filed separately. of course. No dependents.
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WHAT STATE SHOULD I FILE In? WASHINGTON OR MASSACHUSETTS OR Is THERE A DIFFERENCE